EXCHANGE 


BOBI'IZWIW 
'A  "M  ' 


THE  JOHNS  HOPKINS  UNIVERSITY 


The  Absorption  Coefficient  of  Solutions 
of  Cobalt  Chloride  in  Water  and 
Various  Alcohols  for  Mono- 
chromatic Radiation 


DISSERTATION 

SUBMITTED  TO  THE  BOARD   OF  UNIVERSITY   STUDIES   OF   THE 

JOHNS  HOPKINS  UNIVERSITY  IN  CONFORMITY  WITH  THE 

REQUIREMENTS  FOR  THE  DEGREE  OF 

DOCTOR  OF  PHILOSOPHY 


BY 


JOHN  FOSTER  HUTCHINSON 

June  4,  1916 


EASTON,  PA.: 

ESCHENBACH  PRINTING  Co. 
1916 


THE  JOHNS  HOPKINS  UNIVERSITY 


The  Absorption  Coefficient  of  Solutions 
of  Cobalt  Chloride  in  Water  and 
Various  Alcohols  for  Mono- 
chromatic Radiation 


DISSERTATION 

SUBMITTED  TO  THE  BOARD   OF   UNIVERSITY   STUDIES   OF   THE 

JOHNS  HOPKINS  UNIVERSITY  IN  CONFORMITY  WITH  THE 

REQUIREMENTS  FOR  THE  DEGREE  OF 

DOCTOR  OF  PHILOSOPHY 


BY 

JOHN  FOSTER  HUTCHINSON 

June  4,  1916 


EASTON,  PA.: 

ESCHENBACH  PRINTING  Co. 
1916 


The  Absorption  Coefficient  of  Solutions  of 

Cobalt  Chloride  in  Water  and  Various 

Alcohols  for  Monochromatic 

Radiation1 


Experiments  have  shown  that  in  the  case  of  certain 
solutions  the  absorption  of  monochromatic  radiation  may  be 
represented  by  the  formula 

I  =  I0  X  10—' (i) 

where  I0  is  the  original  intensity  of  the  radiation.  I  is  the 
intensity  of  the  radiation  after  passing  through  a  layer  of 
solution  of  thickness  t  millimeters,  and  a  is  a  constant  for  the 
solution  in  question  called  the  absorption  coefficient  of  the  solu- 
tion for  the  specified  frequency  of  radiation. 

Experiments  have  also  shown  that  different  values  of  a 
are  obtained  if  there  is  any  change  in : 

(a)   the  nature  of  the  solvent  or  of  the  dissolved  substance, 

(6)    the  concentration  of  the  solution, 

(c)  the  temperature, 

(d)  the  wave-length  of  the  radiation,  etc. 

To  solve  the  problem  of  light  absorption  in  solutions  it  is 
necessary  to  determine  the  explicit  form  of  the  relation  be- 
tween the  absorption  coefficient  a,  and  the  quantities  of 
which  it  is  a  function.  At  the  present  time  our  knowledge 
is  far  too  meagre  to  indicate  more  than  a  qualitative  idea 
of  the  nature  of  this  relation. 

In  the  present  investigation  a  has  been  measured  in 
those  regions  of  the  spectrum  where  the  pure  solvents  possess 
appreciable  absorption.  It  is  assumed  that  the  total  ab- 
sorption of  the  solution  is  the  sum  of  two  parts,  the  first  being 
the  absorption  due  to  the  presence  of  the  salt,  the  second  being 
the  absorption  due  to  the  pure  solvent.  In  calculating  this 


1  This  is  a  report  bn  part  of  an  investigation  carried  out  with  the  aid  of  a 
grant  from  the  Carnegie  Institution  'of  Washington. 


371461 


second  part,  it  is  assumed  that  the  absorption  due  to  the 
solvent  is  the  same  as  it  would  be  if  there  were  no  dissolved 
salt  present.  We,  therefore,  write 

a  =  Ac  +  a0 

where  a0  is  the  absorption  coefficient  for  the  pure  solvent, 
c  is  the  concentration  in  gram-molecules  of  salt  per  liter  of 
solution,  and  A  is  called  the  molecular  absorption  coefficient 
of  the  salt  in  the  solution.  From  this  relation  we  get 

-.(2) 


The  present  investigation  consisted  of  a  systematic  and 
thorough  study  of  the  absorption  coefficient  a.  This  quantity 
has  been  measured  at  intervals  of  2o/zju  to  4Ojuju  throughout 
the  region  of  the  spectrum  from  600  juju  to  1300/1^  for  many 
solutions.  The  work  has  been  restricted  to  a  study  of  in- 
organic salts  in  aqueous  and  alcoholic  solution.  All  the 
measurements  have  been  carried  out  with  solutions  at  room 
temperature.  The  values  of  a,  when  plotted  as  ordinates 
against  the  corresponding  wave-lengths  as  abscissas,  form  the 
absorption  curve.  For  each  salt  a  series  of  solutions  varying 
in  concentration  from  saturation  to  moderate  dilution  were 
prepared,  and  the  absorption  curve  has  been  drawn  for  each 
solution.  From  the  measured  values  of  a  and  a0,  and  from 
the  known  value  of  c,  A  has  been  calculated  for  each  wave- 
length by  means  of  formula  (2).  The  values  of  A  for  a  given 
wave-length  have  been  plotted  as  ordinates  against  the  corre- 
sponding values  of  c  as  abscissas.  The  curves  thus  formed 
will  be  referred  to  as  the  A-c  curves. 

If  experiments  with  any  solution  show  that  the  relation 
between  a  and  c  is  a  linear  one,  and  therefore  that  A  in  formula 
(2)  is  a  constant,  the  K-c  curves  for  such  a  solution  are 
straight  lines  parallel  to  the  axis  of  abscissas.  Previous 
researches1 2  have  shown  that  in  general  the  K-c  curves  are 
not  straight  lines  parallel  to  the  axis  of  abscissas,  or,  in  other 


1  Sammlung  chemischer  und  chemisch-technischer  Vortrage,  9,  i  (1904). 

2  Proc.  Roy.  Soc.  Edinburgh,  33,  156  (1912-13). 


words,  that  A  is  not  a  constant.1  It  was  the  purpose  of  the 
present  investigation  to  determine  the  form  of  the  A-c  curves. 
The  chlorides,  nitrates  and  sulphates  of  cobalt,  nickel, 
and  chromium,  and  a  few  other  salts,  have  been  studied  in  this 
investigation.  This  paper  is  a  report  on  the  results  of  the 
work  on  a  single  salt,  cobalt  chloride. 

Apparatus — The    apparatus    used    for    determining    the 
light  absorption  coefficient  has  been  developed  by  previous 

workers  in  this  laboratory.2 
The  arrangement  of  the  ap- 
paratus is  shown  in  Fig.  i. 
The  light  from  a  Nernst  glower, 
g,  run  at  no  volts  on  0.8  am- 
pere direct  current  from  a  con- 
stant potential  storage  battery, 
s  was  rendered  parallel  by  a 
;::[-- 3  lens,  fc,  3.8  cm  indiameter  and 
with  a  focal  length  of  20  cm. 
The  light  after  passing  through 
cell  k'  was  focussed  on  the 
slit  A  of  the  spectrograph  by  a 
second  lens,  fc,  3.8  cm  in  diam- 
eter and  with  a  focal  length 
of  20  cm.  A  shutter,  s,  was 
placed  between  the  glower  g 
and  lens  fc,  by  means  of  which 
the  light  could  be  turned  on 
and  off.  The  optical  system 


1, 


A 


Fig.  i 


thus  far  described,  consisting  of  the  glower,  the  two  lenses,  k  and 
fc,  and  the  cells,  was  held  by  a  solid  metal  frame  work,  and 
was  perpendicular  to  the  plane  of  the  drawing  in  Fig.  i .  The 
light  after  passing  through  the  lens  fc  was  reflected  on  to  slit 

1  Beer  has  stated  (Pogg.  Ann.,  86,  78-88  (1882))  as  a  result  of  his  ex- 
periments on  aqueous  solutions  of  inorganic  salts  that  A  is  a  constant  with 
respect  to  c.     This  "law"  of  Beer  has  been  shown  to  be  the  exception  rather 
than  the  rule,  and  therefore  in  this  paper  no  reference  has  been  made  to  "Beer's 
Law." 

2  Carnegie  Inst.  of  Wash.,  Pub.  190  and  230. 


A  by  a  right-angle  glass  prism  (not  shown  in  Fig.  i)  close  to 
slit  A. 

The  spectrograph  consisted  of  the  Littrow  mounting  of  a 
plane  grating.  The  grating  had  a  ruled  area  6  cm  by  7.5 
cm  and  was  ruled  15000  lines  to  the  inch.  The  cone  of  light 
from  slit  A  was  reflected  by  a  right-angle  glass  prism  through 
the  large  achromatic  lens  /3,  10  cm  in  diameter  and  with  a  focal 
length  of  75  cm.  The  spectrum  was  brought  to  a  focus  at 
slit  B.  The  grating  possessed  a  bright  first  order,  and  this 
first  order  spectrum  was  used  throughout  the  present  work. 
The  dispersion  was  such  that  with  slit  B  one  millimeter  wide  a 
"monochromatic  beam"  of  light  containing  a  wave-length 
range  of  20  A,  or  2ju/z,  passed  through.  In  this  work  both 
slit  A  and  slit  B  were  always  one  millimeter  in  width.  The 
correction  for  finite  slit-width  was  negligible.  The  grat- 
ing was  mounted  on  a  turn-table  which  was  rotated  from 
the  outside  by  a  worm-screw,  thus  causing  various  wave- 
lengths to  pass  through  slit  B.  The  monochromatic  beam  of 
light  from  slit  B  was  focussed  by  a  lens,  /4,  35  cm  in  diameter 
and  with  a  focal  length  of  6  cm  on  the  junction  of  the  radio- 
micrometer. 

The  solution  for  which  a  was  to  be  determined  was  placed 
in  two  glass  cells  exactly  alike  in  all  respects,  except  that  one  cell 
was  thin  and  the  other  thick.  The  energy,  I,  of  the  mono- 
chromatic beam  of  light  after  passing  through  the  thin  cell 
containing  a  thickness,  h,  of  the  solution,  and  the  energy,  I', 
after  passing  through  the  thick  cell  containing  a  thickness,  h', 
of  solution,  were  measured  in  arbitrary  units,  i.  e.,  deflections 
of  the  radiomicrometer.  If  the  initial  intensity,  I0,  of  the 
light  falling  on  the  cell  was  the  same  in  each  case 
I  =  I0  X  io~ah 


—ah> 


I-      d  ,  , 

or  a  =  ylogj, (3) 

where  d  and  d'  are  the  deflections  produced  by  I  and  I', 


respectively,  and  /  is  the  difference  in  thickness  in  millimeters 
of  the  two  cells.  This  method  eliminated  all  corrections  for 
reflections  from  the  glass  surfaces,  and  thus  gave  a  directly. 

Results 

Cobalt  Chloride  in  Water  (Figs.  2,  2 a) — Twenty- three  solu- 
tions were  prepared  varying  in  concentration  from  c  =  3.23  to 


600  700  .800  900  1000  1100 


Fig.  2<» 


c  —  o.i.  The  more  concentrated  solutions  were  quite  stable 
and  showed  no  signs  of  decomposition  even  after  standing 
in  the  bottles  for  several  days.  In  the  more  dilute  solutions, 
however,  there  appeared  a  flocculent  precipitate  which  in- 
creased their  absorption  materially.  On  this  account  a 
second  set  of  solutions  whose  concentrations  varied  from 
c  =  i.o  to  c  =  o.i  were  prepared,  and  the  results  of  the 
measurements  of  these  appear  in  the  figure. 

The  absorption  curves  include  the  long- wave  side  of  the 
yellow-green  cobalt  absorption  band  and  the  short-wave 
side  of  the  infra-red  band,  and  show  the  region  of  transmission 
between  the  two  bands.  The  minimum  of  absorption  is  at 

764  MM- 

The  A-c  curves  for  wave-lengths  605  ju JJL  to  7641*1*,  in- 
clusive, which  lie  on  the  edge  of  the  yellow-green  band,  show 
that  A  decreases  in  a  marked  manner  with  dilution,  reaching 
a  minimum  value  at  about  c  =  i.o.  Below  c  =  i.o  A  ex- 
periences a  slight  increase. 

The  A-c  curves  for  those  wave-lengths  in  the  region  of 
transparency,  from  842/4/4  to  979 MM>  are  straight  lines  parallel 
to  the  axis  of  abscissas,  showing  that  in  this  region  A  is  con- 
stant for  all  concentrations.  For  wave-lengths  greater  than 
979  MM>  which  lie  on  the  edge  of  the  infra-red  band,  A  is  a 

TABLE  I 
A  for  Cobalt  Chloride  in  Water 


TTT_.T«    1^i*i  rt~4-l-» 

c  =  0.65 

c  =  3.10 

w  ave-iengtn 

Houston 

From  this  work 

Houston 

From  this  work 

645  MM 

0.041 

0.0340 

— 

— 

684 

0  .  024 

0.0232 

O.200 

— 

720 

0.031 

0.0123 

O.04I 

0.0330 

750 

0.028 

0.0090 

0.037 

0.0150 

794 

0.028 

0.0109 

0.016 

0.0138 

850 

0.028 

0.0147 

0.018 

0.0165 

910 

0.028 

0.0175 

0.029 

0.0198 

980 

0.040 

0.0275 

0.038 

— 

1070 

0.070 

0.0762 

0.074 

— 

constant  within  the  error  of  experiment.  The  two  band 
edges  in  question  are  thus  seen  to  behave  quite  differently 
as  dilution  proceeds.  Houston1  has  drawn  the  absorption 
curves  for  two  solutions  of  cobalt  chloride  in  water;  and  Table 
I  shows  the  comparison  between  Houston's  values  and  the 
values  found  in  this  work. 

The  agreement  between  Houston's  values  and  the  values 
of  A  found  in  the  present  investigation  is  far  from  satis- 
factory. However,  both  sets  indicate  similar  changes  in  A 
with  c. 

Cobalt  Chloride  in  Methyl  Alcohol.     (Figs,  j, 


Seven  solutions  were  prepared  varying  in  concentration 
from  c  =  0.7  to  c  =  o.i.  The  solutions  appeared  to  keep 
very  well,  and  no  such  precipitate  was  formed  as  was  noticed 
in  the  water  solutions.  The  absorption  curves  show  that  the 
character  of  the  absorption  of  the  alcohol  solutions  was  quite 
different  from  that  of  the  water  solutions,  the  absorption 
curve  for  the  alcohol  solution  being  shifted  toward  the  red, 


1  Proc.  Roy.  Soc.  Edinburgh,  31,  521  (1910-11). 


8 


.1400 

.1500 

200 

.1100 

A 

.1000 

.0900 


m  w 


744 


.0700 


.0600 


7 


1056 


0500 


.0400 


.0500 

.oeoo 


.0100 


1018 


so  that  the  minimum  of  absorption  was  now  found  at 
the  shift  thus  amounting  to  about  80  MM-  The  shift  toward 
the  red  of  the  edge  of  the 
band  in  the  green  was  suffi- 
cient to  make  this  band  ab- 
sorb nearly  all  of  the  visible 
red  light.  (Instead  of  speak- 
ing of  the  ' 'shift  of  a  band," 
some  have  preferred  to  speak 
of  the  bands  in  the  different 
solvents  as  entirely  different 
bands.)  As  a  consequence  QSOO 
the  more  concentrated  solu- 
tions appeared  a  deeppurple, 
becoming  more  and  more 
pink  as  the  dilution  in- 
creased. 

The  A-c  curve  for  744 MM 
shows  that  A  decreases  by  a 
large  amount  with  dilution, 
dropping  from  0.128  for  c  — 
0.7  to  0.080  for  e  =  o.i. 
This  is  the  only  A-c  curve 
which  has  been  plotted  for 
a  wave-length  lying  on  the  edge  of  the  red-yellow  absorp- 
tion band,  for  this  edge  is  tremendously  sharp  compared 
to  the  edge  of  the  analogous  band  of  the  water  solu- 
tion. The  A-c  curves  for  the  region  of  transmission, 
764 MM  to  920 MM,  and  for  the  edge  of  the  infra-red  band 
920 MM  to  1 1 34 MM,  show  that  A  for  these  regions  of  the  spec- 
trum remains  approximately  constant  for  all  concentrations. 

Cobalt  Chloride  in  Ethyl  Alcohol.     (Fig.  4) 

Four  solutions  were  prepared  varying  in  concentration 
from  c  =  0.4  to  c  =  o.  i .  A  month  later  a  second  series  of  more 
dilute  solutions  for  which  c  was  0.08,  0.06,  0.05,  0.04,  0.03, 
0.02,  o.oi,  0.005,  were  prepared,  and  their  absorption  curves 


drawn  only  in  the  regions  of  moderate  absorption,  from 
1056 ju/i  to  1134/zju,  and  for  724/4  ju.  In  the  other  regions 
they  either  absorbed  too  much,  or  too  little,  so  that  no  con- 
fidence could  be  placed  in  the  values  of  A. 


800  900  1000  1100  1200  1300/iu 

Fig.  4 

The  absorption  curves  for  the  ethyl  alcohol  solutions  are 
similar  in  then-  general  character  to  those  for  methyl  alcohol. 
The  minimum  of  absorption  occurs  in  the  same  place,  at 
842/1/1,  and  the  steepness  of  the  edge  of  the  bands  is  much  the 
same.  The  ethyl  alcohol  solutions  were  of  a  pure  deep  blue 
in  the  higher  concentrations,  becoming  greenish  blue  as  dilu- 
tion increased. 


10 


The  A-c  curves  for  724  MM  and  744 MM  show  that  A  de- 
creases with  dilution,  and  the  decrease  in  this  case  is  far  greater 
than  in  the  case  of  methyl  alcohol.  For  wave-lengths  764 MM 
to  979 MM  m  the  region  of  transmission,  A  is  fairly  constant. 
For  the  region  on  the  edge  of  the  infra-red  band,  1018  to  1134, 
the  A.-C  curves  show  that  A  increases  with  dilution.  These 
last  mentioned  curves  illustrate  the  magnitude  of  the  error 
in  the  determination  of  A  in  the  case  of  very  dilute  solutions. 

Cobalt  Chloride  in  Propyl  Alcohol.     (Fig.  5) 
Eight  solutions  were  prepared  varying  in  concentration 
from  c  =  0.434  to  c  =  o.io.     The  character  of  the  absorption 


II 

curves  is  the  same  as  that  of  the  ethyl  alcohol  solutions,  the 
minimum  of  absorption  occurring  again  at  842ju/z,  and  the 
steepness  of  the  edges  of  the  bands  being  similar.  The  propyl 
alcohol  solutions  were  also  deep  blue,  becoming  a  greenish 
blue  upon  dilution.  The  absorption  curve  for  c  =  0.434  has 
been  drawn  in  greater  detail,  readings  having  been  taken  at 
every  iojuju. 

The  A-c  curve  for  744  juju,  lying  on  the  edge  of  the  yellow- 
red  absorption  band,  shows  A  to  decrease  greatly  with  dilution. 
This  curve  (and  the  A-c  curves  for  io56/*ju  and  1095^/4) 
have  been  plotted  on  a  scale  of  ordinates  ten  times  as  small 
as  the  other  A-c  curves.  For  wave-lengths  in  the  region  of 
low  absorption,  764 jit/*  to  842juju,  A  is  approximately  con- 
stant, although  in  this  region  the  values  of  a  are  so  small  that 
the  values  of  A  are  liable  to  considerable  inaccuracy.  The 
A-c  curves  for  wave-lengths  920 ju  /*  to  109 5  ju/i,  on  the  edge 
of  the  infra-red  band,  show  that  A  increases  rapidly  with 
dilution. 

Cobalt  Chloride  in  Iso-Butyl  Alcohol.     (Fig-  6) 

Four  solutions  were  prepared  varying  in  concentration 
from  c  =  0.194  to  c  =  0.05.  The  absorption  curves  have  the 
same  character  as  those  for  the  ethyl  alcohol  solutions,  and 
the  color  of  the  solutions  in  the  bottles  was  the  same,  being  a 
deep  blue  which  changed  to  a  greenish  blue  upon  dilution. 
In  preparing  the  solutions  the  usual  precedure  was  followed, 
namely,  to  make  the  dilutions  by  addition  of  the  pure  alcohol 
to  the  saturated  mother  solution.  It  was  found  that  a  pre- 
cipitate appeared  immediately  upon  dilution.  The  solu- 
tions were  then  filtered,  and  the  concentrations  measured  by  a 
determination  of  the  density.  The  value  of  the  concentration 
determined  in  this  way  was  found  to  agree  within  the  error  of 
experiment  with  the  concentration  calculated  from  the  known 
amount  of  dilution.  This  showed  that  the  loss  by  precipitation 
was  either  negligible,  or  that  the  precipitate  contained  nearly 
equal  parts  of  cobalt  chloride  and  iso-butyl  alcohol.  The 
filtered  solutions  appeared  quite  free  from  any  visible  particles. 


12 


In  the  cells  they  had  a  somewhat  cloudy  appearance,  sugges- 
tive of  a  colloid  condition.  They  showed  slightly  a  Tyndall 
cone  in  blue  light.  An  examination  of  these  freshly  filtered 
iso-butyl  alcohol  (and  also  the  iso-amyl  alcohol)  solutions 
with  the  ultramicroscope  showed  that  they  were  not  colloidal 
in  nature,  but  that  they  contained  a  number  of  particles. 
Whether  these  particles  were  newly  formed  precipitate,  or 
some  impurity,  is  unknown. 


1500/ujA 


The  A-c  curves  for  73 4 MM  and  744 MM,  wave-lengths  lying 
on  the  edge  of  the  yellow-red  absorption  band,  show  again 
that  A  decreases  rapidly  with  dilution.  For  the  wave-lengths 
754 MM  and  764 MM  in  the  region  of  transmission  A  is  a  con- 
stant. The  behavior  of  the  edge  of  the  infra-red  band  is 
similar  to  the  case  of  the  propyl  alcohol  solutions,  for  A  in- 
creases with  dilution,  as  shown  by  the  rise  in  the  K-c  curves 
for  wave-lengths  IOISMM  to  1133 MM- 


Cobalt  Chloride  in  Iso-amyl  Alcohol.     (Fig.  7) 

Six  solutions  were  prepared  varying  in  concentration 
from  c  =  0.064  to  c  =  o.oio.  The  solutions  in  the  bottles 
were  of  a  deep  blue  color  in  the  higher  concentrations,  which 
changed  to  a  greenish  blue  upon  dilution.  The  general 
character  of  the  absorption  curves  is  the  same  as  that  of  the 
ethyl  alcohol  solutions. 


The  iso-amyl  alcohol  solutions  exhibited  the  same 
phenomenon  of  precipitation  upon  dilution  as  has  been  de- 
scribed in  the  case  of  the  iso-butyl  alcohol  solutions.  They 
also  had  the  same  appearance  in  the  cells,  and  under  the  ultra- 
microscope. 

A  study  was  made  of  the  precipitate  which  was  thrown 
down  in  these  solutions,  for  the  deposit  in  the  case  of  the 
iso-amyl  alcohol  solutions  was  more  abundant  than  in  the 
case  of  the  deposits  in  the  other  cobalt-chloride  solutions. 
The  solution  was  allowed  to  stand  for  two  weeks,  and  then  the 
precipitate  was  filtered  off.  This  precipitate  consisted  of 


14 

blue  needle  crystals  mixed  with  a  flocculent  scale-like  residue. 
Analysis  showed  that  in  this  flocculent  residue  there  was 
present  54  percent  by  weight  of  cobalt  chloride.  If  this 
precipitate  was  a  compound  of  the  cobalt  chloride  and  the 
alcohol,  this  percentage  of  the  chloride  would  indicate  that  the 
compound  contained  two  molecules  of  the  chloride  to  three 
of  the  alcohol. 

The  A-c  curves  for  the  edge  of  the  yellow-red  absorption 
band,  at  7 14 MM  and  724  MM>  show  that  A  decreases  with 
dilution.  In  the  region  of  transparency  between  the  two 
bands  A  is  constant,  as  shown  by  the  A-c  curves  for  734 MM 
and  744 MM-  The  A-c  curves  for  the  edge  of  the  infra-red  band 
show  that  A  increases  very  rapidly  with  dilution. 

Discussion  of  Results  with  Cobalt  Chloride 

This  study  of  cobalt  chloride  in  water  and  alcoholic  solu- 
tion brings  out  the  following  facts : 

In  the  region  of  wave-lengths  lying  on  the  long  wave- 
length edge  of  the  yellow-red  absorption  band  the  A-c  curves 
show  that  A  decreases  with  dilution.  The  decrease  in  A 
observed  in  the  case  of  the  water  solution  is  considerable, 
and  in  the  case  of  the  alcoholic  solutions  this  decrease  becomes 
more  and  more  marked  as  the  molecular  complexity  of  the 
alcohol  increases.  Jones  and  Anderson1  studied  solutions 
of  cobalt  chloride  in  water,  methyl  alcohol,  and  ethyl  alcohol. 
Plates  2,  4,  and  5  of  their  paper  showed  that  for  wave-lengths 
on  the  red  edge  of  the  yellow-red  absorption  band  A  de- 
creased with  dilution,  and  also  showed  that  this  decrease  was 
much  more  marked  in  the  case  of  the  alcoholic  solutions  than 
in  the  water  solution.  This  is  in  accord  with  the  facts  brought 
out  by  the  measurements  discussed  in  the  preceding  para- 
graphs. 

In  the  region  of  low  absorption  between  the  two  bands 
it  is  concluded  that  A  is  constant.  As  has  been  mentioned 
already,  in  the  section  concerning  cobalt  chloride  in  propyl 
alcohol,  the  values  of  a.  for  the  region  between  the  two  bands 

1  Carnegie  Inst.  of  Wash.,  Pub.  no. 


15 

are  so  small  that  the  values  of  A  are  in  many  cases  worthless. 
In  the  region  of  wave-lengths  lying  on  the  edge  of  the 
infra-red  band  A  experiences  deviations  from  a  constant 
value,  and  again  these  deviations  show  a  certain  regularity 
concomitant  with  the  increasing  molecular  complexity  of  the 
solvent.  In  this  region  A  is  nearly  constant  for  the  water 
solutions,  but  increases  with  dilution  for  the  alcohol  solu- 
tions, the  increase  becoming  greater  as  the  molecular  weight 
of  the  alcohol  increases. 

Conclusion 

The  relation  between  A,  the  molecular  light  absorption 
coefficient  of  the  solution,  defined  by  equation  (2),  and  c,  the 
concentration  of  the  solution  in  gram-molecules  of  salt  per 
liter  of  solution,  has  been  determined.  It  has  been  found 
that  in  general  A  is  not  a  constant.  In  certain  cases  A  de- 
creases with  dilution,  in  other  cases  A  increases  with  dilution, 
and  in  still  other  cases  as  dilution  proceeds  A  decreases  to  a 
minimum,  and  then  increases  again.  Another  possible  com- 
bination, namely,  that  A  should  increase  to  a  maximum  and 
then  decrease,  was  not  met  with. 

At  present  there  is  no  adequate  theory  to  explain  the 
facts  which  have  been  recorded  here.  The  fact  that  A  varies 
with  c  has  been  probably  correctly  attributed  by  Jones  and 
Anderson1  and  others  to  the  formation  of  complexes,  which 
were  considered  to  be  loose  chemical  compounds  of  molecules 
of  the  salt  with  molecules  of  the  solvent.  Undoubtedly  the 
changes  in  A  with  c  observed  in  this  investigation  may  be 
explained  in  a  qualitative  manner  by  the  hypothesis  of  com- 
plexes, or  "solvates"  as  they  have  been  called.  But  before 
it  can  be  useful  for  the  interpretation  of  quantitative  data, 
the  solvate  hypothesis  must  be  couched  in  mathematical 
terms. 

The  Johns  Hopkins  University 
May  10,  iQi6 


1  Loc.  cit. 


BIOGRAPHICAL  NOTE. 

John  Foster  Hutchinson,  son  of  Edwin  James  Hutchinson, 
and  Jennie  (Lilly)  Hutchinson,  was  born  in  Tonawanda,  N.  Y., 
on  June  6,  1893.  His  early  training  was  received  in  Ferguson, 
S.  C.  In  1909  he  entered  The  Military  College  of  South 
Carolina,  and  in  1913  was  admitted  to  the  degree  of  Bachelor 
of  Science.  In  1914  he  received  the  degree  of  Master  of  Arts 
from  the  College  of  Charleston.  He  entered  the  Johns  Hopkins 
University  in  1914  as  a  graduate  student,  making  Chemistry 
the  principal  subject,  Physical  Chemistry  the  first  subordinate, 
and  Mineralogy  the  second  subordinate.  He  attended  grad- 
uate courses  given  by  Professors  Jones,  Morse,  Reid,  Love- 
lace, Frazer  and  Swartz.  He  was  the  holder  of  Hopkins 
Scholarships  during  the  years  1914-1915  and  1915-1916. 


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